The physical separation of three subpopulations of granulocyte/macrophage progenitor cells from mouse bone marrow

The heterogeneity among progenitor cells of granulocytes and macrophages capable of forming colonies in vitro (CFU-c) is analysed. If specific culture conditions and stimuli are used, it is possible to discriminate among three subpopulations of CFU-c. CFU-c directly responding to CSF prepared from pregnant mouse uteri are characterized by a density of 1.075 g.cm-3. The G1-phase cells of this CFU-c subpopulation have a sedimentation rate of 4.8 mm.h-1. CFU-c of two additional subpopulations are induced to proliferate by enhancing factors present in serum of mice injected with endotoxin 18 hours earlier and in lysate of rat erythrocytes. CFU-c responding to postendotoxin serum have a density of 1.070 g.cm-3 and a sedimentation rate of 4.3 mm.h-1 (G1 cells). The CFU-c responding to erythrocyte lysate have a density of 1.080 g.cm-3 and a sedimentation rate of 5.3 mm.h-1 (G1 cells). The calculated diameters of G1-phase cells of these three CFU-c subpopulations range from 7.4 to 7.6 micron and are not significantly different. It is proposed that the three CFU-c detected represent three sequential maturation stages of granulocyte/macrophage progenitor cells. These cells are similar in size but increase in density (1.070 g.cm-3 to 1.080 g.cm-3) as they mature.